1. Technical Field
This invention relates to a printed board and a method for producing the printed board. In a printed board to which a bus bar is attached, embodiments of the present invention can prevent a failure in the connection between the bus bar and the printed board.
2. Background Art
An electrical junction box is mounted on a vehicle, such as a motor vehicle. Electronic parts to be mounted on the vehicle are arranged on a printed board. Based on the rapid increase in the amount of electronic parts, the electrical junction box generally contains a printed board provided with electronic parts. In some electric junction boxes, a bus bar is arranged on a printed board as an internal circuit. The bus bar and printed board are interconnected by a reflow process. In the reflow process, bonders (e.g., solder) are joined to the bus bar and printed board. The bonders, bus bar and printed board are placed in a reflow furnace under a high temperature atmosphere, and the bonders are melted to interconnect the bus bar and the printed board.
Some bus bars contain one or more terminals. When the bus bar and printed board are bonded by the reflow process, the terminal can dislodge and float upward from a through-hole in the printed board due to a difference in coefficient of thermal expansion between the printed board and the bus bar under the high temperature atmosphere. This dislodging can occur unless the terminal of the bus bar is securely held in the through-hole in the printed board. If such a condition occurs during melting of the bonders, the bus bar cannot be reliably bonded to the printed board and a failure in connection between them will occur. Accordingly, in the reflow process, it is necessary to carry out bonding work while the bus bar is positively held on the printed board so that the bus bar does not float up from the printed board.
There is a related-art bonding method in which a bus bar is prevented from falling off of a printed board by soldering the bus bar and the printed board after a portion of one or more of the terminals of the bus bar are pressed into a portion of one or more through-holes.
However, in the case where all of the terminals are pressed into all of the through-holes, respectively, it is possible that some terminals cannot be inserted into the through-holes based on small tolerances between the terminal of the bus bar and the through-hole in the printed board. On the other hand, in the case where a part of terminals are pressed into a part of through-holes, respectively, the other terminals except the terminals pressed in the through-holes tend to float up from the printed board based on a difference in the coefficient of thermal expansion of the printed board with respect to the bus bar when the printed board is exposed to a high temperature in a reflow furnace. In this case, the terminals are secured to the printed board in a state of floating-up. Consequently, in either case, a failure will occur in connection between the bus bar and the printed board.
In another related-art bonding method, a bus bar is arranged on one side of a printed board and a terminal of the bus bar is inserted into a through-hole in the printed board. Subsequently, a jig holds the bus bar on the printed board to prevent falling-off, and the printed board along with the jig is conveyed into a reflow furnace to melt solder, thereby interconnecting the bus bar and printed board.
In this case, since the solder is bonded on the jig, it is necessary to clean the jig. Furthermore, since the jig is exposed to a high temperature atmosphere, a new jig is required for every printed board. This will require a number of spare jigs and thus will increase cost.
In order to overcome the above problems, there is a bonding method in which after a terminal of a bus bar is inserted into a through-hole in a printed board, a distal end of the terminal is clinched or bent onto the printed board to prevent the terminal from falling off from the printed board and then a soldering step is effected.
JP 2006-60140A1 discloses a soldering method wherein a distal end of a terminal to be inserted into a printed board is clinched and soldered to the printed board. As shown in FIG. 9 of the present application, a pair of leading terminal portions 2a of an electrical part 2 are inserted into through-holes in a printed board 1, projecting ends 2b of the leading terminal portions 2a protrude out on the opposite side of the printed board 1, the projecting ends 2b are bent at an angle of about 90 degrees by clinching, and a solder H electrically interconnects the printed board 1 and the electrical part 2.
However, since the leading terminal portions 2a are bent at an angle of about 90 degrees, the projecting ends 2b of the leading terminal portions 2a come into contact with the printed board 1, thereby damaging the printed board 1.